about 50k miles, ran perfectly for a long time. Suddenly started to have some problems: rough idle, sluggish acceleration and finally one cylinder cut off.

At the same time I replaced the fuel filter (pump was making some high pitch noise) than replaced a coil and all spark plugs, plus two spark plug wires.
Engine runs so-so, but still far from the perfect run.

Any idea what else to do?

The garage mechanics are telling me that everything is OK, but I know the vehicle is far from beeing perfect :)

There may be some inlet manifold switching flaps, I do not know about the 320, but the newer 350 motor has 'tumble flaps' for each cylinder and an EGR flap either for each cylinder or for each bank. If any of these valves stick open, closed or partially open the performance will be obviously bad.

You could try gas additive which frees stuck valves or dirty injectors - maybe other reader will chime in with their experiences.

The 112 engine also has the manifold "flaps". They are used to create a variable intake length so that the torque curve can be manipulated for better performance. Itâ€™s doubtful that any malfunction of these flaps could cause much of a problem in only one cylinder.

Thank you for sharing your experience on this subject.
I just have more lights into it.
Got the car from mechanic last night. They replaced ALL the high voltage wires and cleaned injectors.

While talking to the mechanic, he said the missfire was reported on diferent cylinders, not just same one over.

I did mentioned they replaced a fuel filter - it was a new type filter - with the whole upgrade kit - and this filter caused a fuel pressure drop by 5 psi. So switching back to the old type filter helped with the better fuel delivery.

While getting on a highway I got Engine Check light ON again. THis time I was at the time when mechanic was checking the faulty codes. The code was missfire on cylinder 2 and possible TWC damage.

about 50k miles, ran perfectly for a long time. Suddenly started to have some problems: rough idle, sluggish acceleration and finally one cylinder cut off.

At the same time I replaced the fuel filter (pump was making some high pitch noise) than replaced a coil and all spark plugs, plus two spark plug wires.
Engine runs so-so, but still far from the perfect run.

Any idea what else to do?

The garage mechanics are telling me that everything is OK, but I know the vehicle is far from beeing perfect :)

Use OBDII scanner to check for faults. do you have a check engine light on?

if not, then it maybe during the coil pack / wire install that they messed it up big time and now you have missfires.

I would like to thank you all who responded to my problem. It has been more than a Week passed since I replaced the Air Flow Meter and ALL problems dissapeared.

I am glad I posted this problem here on the forum.
I was going nutts trying to figure out what might be wrong.

Lets summarize:
1) it started with whisseling fuel filter
- replaced an original fuel filter with the upgraded one (the whole kit)
2) sluggish acceleration - fuel pressure reduced by 5 psi
3) missfire code on various cylinders
4) disconnected single cylinder (2 and later 5)
- replaced all the spark plugs, high voltage wires
- replaced the fuel filter to the old style - (pressure back to normal)
5) missfire still existed, and error code showed again faults on various cylinders with error code on demaging TWC
- replaced Air Flow Meter

NO MORE MISSFIRES ERRORS

I am glad I did not listen to the mechanic who suggested to replace TWC ($3k brrrrr)